The present invention relates to improvements in apparatus for manipulating paper sheets or the like, and more particularly to improvements in apparatus for selectively transporting a stream of partly overlapping paper sheets or the like from a first path into one of several additional paths.
It is well known to assemble printed sheets, which issue from a printing machine and are thereupon folded in a folding machine, into a continuous stream wherein the sheets partly overlap each other (such stream is known as a scalloped stream). In a modern bookbinding plant, the scalloped stream is automatically transported to one or more further processing stations, for example, in a manner as disclosed in the aforementioned copending application Ser. No. 908,546. The transporting system normally comprises several belt or chain conveyors, and the junctions between the neighboring conveyors are provided with switching devices which enable a preceding conveyor to deliver sheets to any one of several next-following conveyors. For example, the preceding conveyor can deliver sheets to a first next-following conveyor which, in turn, delivers the sheets to a processing station, or to a second next-following conveyor which can deliver sheets into a magazine. It has been found that the heretofore known switching devices often present problems, especially when the scalloped stream is or should be transported at an elevated speed and the number of sheets which enter a selected additional path downstream of the (first) path along which the preceding conveyor delivers the sheets should not deviate from a predetermined number.
The apparatus which is disclosed in the copending application Ser. No. 908,546 comprises means for breaking up a continuous scalloped stream into discrete streams of identical length and containing identical numbers of partially overlapping sheets. Such discrete streams are manipulated not unlike the freight trains on the slidings of a railroad station. The apparatus includes switching devices which can divert discrete streams into different additional paths, for example, into additional paths preceding the magazines of various processing machines. The means for dividing a continuous scalloped stream into discrete streams of predetermined length includes a counter which actuates a braking device serving to engage the adjacent sheet of the continuous stream and to temporarily hold the engaged sheet against forward movement. The sheets which follow the engaged sheet pile up behind the braking device to form a stack which constitutes the leader of the respective discrete stream. A clearance or space develops between the sheet which is held by the braking device and the preceding sheet (i.e., the last sheet of the preceding discrete stream). The width of the clearance is determined in advance, i.e., it depends on the speed of the conveyor which delivers the continuous stream and on the length of the interval of engagement between a selected sheet and the braking device. A clearance is located in the region of the switch which follows the braking device (or in the region of a switch further downstream of the braking device) whenever the switch is moved to a different position to divert the freshly formed discrete stream into a selected path. The drawbacks of relatively wide clearances between successive discrete streams are numerous and serious. Thus, the leader of each discrete stream accumulates a relatively large number of fully or nearly fully overlapping sheets because such number is directly proportional to the width of the clearance between two successive discrete streams. The pileup at the leading end of a discrete stream is likely to cause problems during introduction of discrete streams into selected additional paths and may interfere with proper singularizing of sheets in the processing machines which follow. On the other hand, presently known switches cannot operate properly unless the width of the clearances between neighboring (successive) discrete streams at least approximates a predetermined minimum value which is sufficient to cause the accumulation of relatively large piles of fully or nearly fully overlapping sheets at the leaders of the discrete streams. The accumulations of fully or nearly fully overlapping sheets at the leaders of successive discrete streams can interfere with introduction of discrete streams into the magazines of various processing machines.
U.S. Pat. No. 2,815,949 discloses an apparatus wherein the junction between a preceding elongated path and the next-following elongated paths accommodates a tongue-like flap which can descend into the space between the elongated paths and is located upstream of a belt conveyor. The flap can be moved with the belt conveyor to advance along an arcuate path. One of the aforementioned elongated paths for the scalloped stream is substantially tangential to such arcuate path. When the flap descends, it penetrates into the scalloped stream of paper sheets and causes the oncoming sheets to change the direction of their movement. When the flap has deflected a requisite number of sheets into a selected elongated path, it is retracted upwardly and above the junction, together with the associated belt conveyor (again along the aforementioned arcuate path), so that the scalloped stream can advance in the original direction. A drawback of the just described patented apparatus is that the mass of moving parts (flap and the belt conveyor) is quite substantial so that the speed of the scalloped stream cannot exceed a relatively low value if the flap is to find its way between two neighboring sheets of the travelling stream. Furthermore, the energy requirements of means for moving the relatively large masses along the aforediscussed arcuate path are quite substantial and the system for guiding the flap and the belt conveyor along the arcuate path is complex and expensive.
Swiss patent application Ser. No. 6768/77 discloses an apparatus wherein the junction between several neighboring paths for a scalloped stream includes a step and a conveyor belt which slopes upwardly along and is spaced apart from the step. The gap between the conveyor and the step can be bridged by a tongue-like flap whose mass is small so that it can be caused to rapidly penetrate into the scalloped stream in the region of the step. The arrangement is such that the first stage of movement of the flap into the stream takes place at a high speed. When the flap completes the deflection of a given number of sheets into a different path, the restoration of the original condition (i.e., the travel of sheets into the previously selected path) is effected as follows: the conveyor belt and the step are abruptly lifted in parallelism with the slope of the conveyor belt so that the last sheet of the deflected portion of the scalloped stream is rapidly pulled above the junction. This apparatus allows for rapid changes in the direction of transport of the stream and, therefore, the stream can be advanced at a very high speed. However, the initial as well as maintenance cost of the apparatus is extremely high so that the use of such apparatus in production lines or elsewhere is warranted only under certain exceptional circumstances.